Fan casing



Aug. 29, 1939. K. D. MCMAHAN 2,171,341

FAN CASING Original Filed June 1, 1936 Inventor: Kenton D. Mc Mahan,

His Attorn e Patented Aug. 29, 1939 UNITED STATES FAN CASING Y Kenton D.McMahan.

Schenectady, N. Y., as-

signor to General Electric Company, a corporation of New York Originalapplication June 1, 1936, Serial No.

82,780. Divided and this application April 1,

1938, Serial No. 199,462

2 Claims.

This application is a division of my application Serial No. 82,780,filed June 1, 1936. I

The present invention relates to casings for centrifugal fans of thetype having a passage 5 around the fan to which air is discharged and acut-off directing the air to a discharge opening.

The object of my invention is to provide an improved construction in fancasings having a cut-off decreasing the noise.

In the accompanying drawing, Fig. 1 is an end view .of my improved fancasing, and Fig. 2 is an end view of a modification.

Referring to the drawing, there is shown a fan casing or scroll I havingan intake opening 2 and an exhaust opening3. Mounted within the casingis a fan wheel 4 consisting of a'hub 5 to which is secured a pluralityof blades 6 of the type described and claimed in my application SerialNo. 82,780, filed June 1, 1936, extending axially therefrom. Mounted inintake opening 2, is a curved orifice ring I which serves to provide asmooth curved surface to the entering air to prevent any noise by theimpinging of moving air against a sharp edge. Cooperating with orifice lto provide a smooth path within the fan casing is a shroud ring' 'dwhichis secured to blades 6. Orifice and shroud rings 1 and 8 are of theconstruction clearly disclosed in my above application. Shroud ring 5 isformed as a substantial continuation of orifice l and curves inwardlyand outwardly in the direction in which air moves over this part of thefan but of necessity is spaced from the orifice 'l a sufiicient distanceto provide the necessary clearance between a stationary and a movingpart. In the exhaust opening 3 a out-01f 9 is provided which extends asufiicient distance within the opening 3 to prevent any eddies orreverse fiow within the exhaust opening. The shape of the cut-off is, ofcourse, subject to a great deal of modification. Cut-oif 9 is formed ofa plate l separated from the wall of the casing having a plurality ofperforations ll. Within the space or chamber between the plate I!) andthe wall of casing, felt or other sound deadening material I! isprovided. The perforated plate It and sound deadening material l2located at the cut-oil serve to eliminate much of the noise originatingfrom the, impinging of air against the cut-off at its source. As shownin Fig. 2, I may also accomplish this same result by using a cut-offwith a space 13 between a solid plate I4 and the wall of the casing withan opening l at the inner end forming an air column acting as a cushion.The air column also acts as a sound filter of the air column type. Ihave found that the location of sound deadening material or an aircushion, or a sound filter, or any combination thereof, at the cut-offcan more effectually eliminate this noise than by any means located at adifferent point,

The fan wheel 4 is connected to a source of power, not shown, such as anelectric motor. The operation of the fan is described fully in myapplication Serial No. 82,780, filed June 1, 1936. For the purpose ofthe present invention it is suflicient to state that upon rotation ofthe fan, air is drawn axially into the intake opening 2 by the suctionof the fan and by the forwardly curved front ends I6 of the fan bladesand is discharged in a radial direction between the fan blades. For thepurposes of the present invention, the construction of the fan is notimportant, that is, any centrifugal fan could be substituted for the fanillustrated.

The air, in passing between two adjacent blades, is acted upon as thoughthe blades were a nozzle taking air in at the intake edges anddischarging it at the exhaust edges l'l.v The discharge from each nozzleformed by adjacent blades is in the form of a jet of air which may varyin velocity throughout the nozzle discharge area. These successive jetsimpinging against the walls and cutoff of the casing produce a vibrationhaving a frequency equal to the number of blades times the number ofrevolutions of the fan wheel per unit of time. may have one or moreharmonics of this frequency. This vibration produces a noise theintensity of which depends upon the variation in the magnitude of theair velocity between successive Jets.

The location at the cutofl of sound deadening material or an air cushionor other sound reducing means reducesany noise which may be produced byan uneven discharge from the fan. I find that the noise reduction bylocating the sound deadening material or sound reducing means at thecutoff is disproportionately greater than the noise reduction obtainedby sound deadening material or sound reducing means located elsewhere.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a centrifugal fan casing having an inlet opening andan outlet opening, a centrifugal fan mounted in said casing, and acut-off located in said outlet formed of perforated metal walls spacedfrom the outer walls of said casing, to provide a chamber and having theperforations presented to the air stream moved by the fan.

2. In combination, a centrifugal fan casing having an inlet opening andan outlet opening, a centrifugal fan mounted in said casing, a cut-offlocated in said outlet formed of perforated metal walls spaced from theouter 'walls of said casing, and sound deadening material between thewalls of said casing and said perforated walls.

KENTON D. MCMAHAN.

The vibration

